The invention relates to a system and computer program product for requesting a copy of data from one virtual tape server (VTS) to another VTS in a storage system including multiple VTSs.
FIG. 1 shows a storage system (storage domain) in which two or more VTSs are IP-connected. The space of this storage system is called “grid domain.” Each VTS is positioned as a cluster (Distributed Cluster) as a distributed storage element in the domain.
The domain is required to have a basic function such as doubling or tripling of data to meet requirements for data recovery in disasters. In order to ensure data integrity, it is necessary for each cluster in the domain to have the same data redundantly. The data redundancy enables data copies (data replication) between clusters connected through an IP network, i.e., between virtual tape servers. Specifically, data duplication or the like means replication of a collection of logical blocks, such as virtual logical volumes, through the IP network.
In a virtual tape server, a direct access storage device (DASD) is used to emulate tape drives and tape cartridges. The DASD consists of numerous interconnected hard disk drives. A host system performing I/O operations with respect to tapes in fact performs I/O operations with respect to a set of hard disk drives that emulate tape storage. The virtual tape server connects the DASD with a tape library provided with numerous tape cartridges and tape drives.
The host makes a request to access a tape volume. The virtual tape server intercepts the tape request and accesses the volume in the DASD. If the volume is not in the DASD, the virtual tape server recalls the volume from the tape drive to the DASD. The virtual tape server can respond to host requests for volumes in tape cartridges from the DASD substantially faster than responding to requests for data from tape drives. Thus, the DASD functions as a tape volume cache for volumes in the tape cartridge library.
A virtual tape storage system (or a storage system) can combine two or more virtual tape servers. In a storage system environment, two or more virtual tape servers, each integrated with a separate tape library, can access and store the same data volume. If an operation to recall a file from one virtual tape server fails, then the file can be recalled from another virtual tape server.
This redundant architecture provides data duplication improved to enable use of data and tape in the event a tape or VTS is damaged. Therefore, when the host system writes to a storage device, the data is saved on both virtual tape servers according to user settings.
Writing to both virtual tape servers simultaneously results in the waste of system resources. When the host closes a logical volume, a virtual tape controller connecting two virtual tape servers writes the logical volume to one of the virtual tape servers. This controller acts as an intelligent switch between the two virtual tape servers, and transparently connects the host computer with the virtual tape servers. Then, the logical volume is copied by the virtual tape controller from one virtual tape server to the other virtual tape server.
Copy processing between virtual tape servers can be performed in an immediate synchronization (Run) mode or a Deferred mode based on user preferences. For enterprises that operate on a cyclical basis, a host user will often set backup processing to be performed at a later time. For example, an enterprise may desire higher peak host I/O performance for primary job processing and not desire to have the backup process slow down their computers.
Japanese Patent Application Publication No. 2003-067248 provides an improved method to copy data from a virtual tape server to another virtual tape server in a conventional peer-to-peer environment. In this technique, every time when a data set is modified or created, a flag is used for indicating whether the data set necessitates to be copied from a memory device to another. If the only copy of the data exists on a physical tape in a tape library, backing up from a tape drive causes large delays in the overall processing. However, when multiple source virtual tape servers (VTSs) exist, these VTSs may be busy in processing jobs in progress. Further, the optimum copy source VTS may not be selected because the states of copy jobs being performed by the source VTSs are unconsidered in the entire system.
It is desirable to be able to select an optimum source VTS from among multiple VTSs when one target VTS requests a data copy in a storage system that includes multiple storage devices.